1. The Field of the Invention
The present invention relates to granular flame retardant agents, to a process for preparing the same, to a method for imparting flame-retardant properties to plastic materials using said agents, and to flame-retarded plastic materials obtained thereby.
More particularly, the present invention refers to the use of halogenated hydrocarbon flame retardant agents, alone or in admixture with organic flame-retardant agents and synergists.
2. The Prior Art
It is well known in the art to use halogenated hydrocarbons to impart flame-retardant (FR) properties to flammable plastics. Examples of commercially available FR agents are Decabromodiphenyl oxide, Penta- and Octabromodiphenyl oxide, Hexabromocyclododecane and Tetrabromobisphenol A. It is also known that it is possible to employ mixtures of two or more of such halogenated hydrocarbons, which may be both in solid form or not, and/or mixtures which comprise inorganic or synergistic FR agents, such as antimony oxide or melamine isocyanurate. Non-solid FR compounds comprise, for instance, pentabromodiphenyl oxide. Other various additives are also often employed in admixture with the FR composition, such as binders or carriers, lubricants, smoke suppressors, anti-dripping agents, such as DPFA, and thermal stabilizers.
The halogenated FR compositions, however, are usually in fine powder form which presents several problems. Dispersion of the FR compound within the processed plastic is often nonhomogeneous, pollution problems due to dust formation are severe and certain additives, e.g., antimony oxide, are toxic. Therefore, several approaches have been tried in order to avoid direct use of FR compositions in powder form, for instance, by preparing master batches of the plastic containing high concentrations of FR composition; or colloidal suspensions of the FR compounds are prepared, which are then mixed with the monomer, or binders are used in order to prepare agglomerates of FR compounds.